The invention relates to an apparatus for circumferentially homogenizing temperatures of a ferrule of a component traversing the upper slab of a nuclear reactor.
More specifically, the present invention relates to an apparatus of this type applied to the case of components (circulating pumps, intermediate exchanger) mounted in a fast nuclear reactor cooled by a liquid metal, said reactor being of the integrated type.
In order to provide a better understanding of the problem solved by the present invention, reference is advantageously made to the attached FIGS. 1 and 2, which respectively show a fast neutron reactor of the integrated type in vertical section and a detailed view showing how a pump or intermediate exchanger traverses the slab.
FIG. 1 shows in simplified form the main reactor vessel 2 suspended on the upper concrete slab 4 provided with its system or rotary plugs 6. The main vessel 2 contains the inner vessel 8, which in turn contains the core 10 and the hot liquid metal (e.g. liquid sodium) leaving the core, the liquid metal level being designated by N. Above level N and below slab 4 there is an inert covering gas cushion 11 the gas being for example argon. The hot liquid metal enters intermediate exchangers such as 12, which are suspended on slab 4 and which traverse the latter by not shown cylindrical passages. In a similar way, circulating pumps such as 14 are suspended on slab 4 and traverse the latter by cylindrical passages 16. The invention relates to the problems linked with the traversal of the said slab.
FIG. 2 shows in a more detailed manner the passage of a pump 14 through slab 4. Pump 14 is surrounded by a pump ferrule 14a and slab 4, more particularly level with passage 16 is covered by a sheet 18. The slab is cooled by water pipes 20. Between pump ferrule 14a and the covering sheath 18, there is an intermediate ferrule 22 defining an outer annular space 24 and an inner annular space 26 (the same applies for the passage of an intermediate exchanger). The outer space 24 is insulated from the gaseous cover 11 by a hydraulic joint system (liquid sodium) with a container 28. Thus, there are no problems for the outer space 24, which is insulated from the remainder of the gaseous mass. Inner space 26 communicates with the gaseous cover 11.
Inner space 26 contains "open" thermosiphons, which are supplied by the inert gas in cover 11. These thermosiphons have an upward flow of hot gas and a downward flow of cool gas. Their characteristics are dependent on parameters which are at present not well known.
In the ferrule of the component, (intermediate exchanger or pump) these thermosiphons produce thermal indentations, which can be displaced in a circular manner (in a horizontal plane) and which thus create thermal cycles prejudicial to the good mechanical behaviour of the corresponding ferrules.
It is therefore necessary to eliminate or at least reduce these circumferential thermal gradients. For example, in the case of the French Super Phenix reactor, this circumferential gradient on the pump ferrule is estimated to be 200.degree. C.
One solution would involve choosing all the ferrules with a material having a high thermal conductivity. However, such a solution is unacceptable. On the one hand, this is because the choice of such a material is considerably limited for cost and mechanical behaviour reasons and on the other and in particular because it is necessary to maintain a high vertical thermal gradient between the space 11 or the roof of the pile and the top of the slab 4. Thus, the upper end of the slab must be kept at a maximum temperature of approximately 50.degree. C.